The display probably exists just because soldiers need that stuff, as a practical matter.

When they're required to be in uniform, then that's a requirement.

So if yesterday a uniform got ruined (by whatever mechanism that happens -- shit does happen to clothes sometimes), then today they can scrounge together another one.

Or they put together a spare one.

Or whatever.

(But it certainly is romantic to think that extra uniform parts exist for sale primarily to give as keepsakes to the Betty Whites of the world.)